The long term evolution (abbreviated as LTE) network is consisted of E-UTRAN (Evolved UTRAN) base stations eNBs (Evolved NodeB) and an evolved packet core (abbreviated as EPC), which has a flat network structure.
In the cellular cell system, when a user moves, it is unavoidable that the user will move from one cell to another cell, which causes cell reselection or cell handover. For example, when a user moves during a phone call from the coverage of one cell to the coverage of another cell, in order to make the call uninterrupted, it is required for the user to be able to automatically switch between cells. The network side decides which cell the user switches to and when to switch, etc. According to the attachments of the cell before the handover and the cell after the handover, the handover can be divided into intra-cell handover, inter-cell handover in eNB, inter-eNB handover, handover between different access systems, etc. And the above various handover processes can be understood by referring to the process of inter-eNB handover. As shown in FIG. 1, it includes the following processing:
Step 101: UE reports a downlink measurement result to a serving base station (eNB1).
Step 102: eNB1 makes a handover selection and completes the handover preparation process with the handover target side eNB2.
Step 103: eNB1 informs via a signaling the UE to switch.
Step 104: the UE initiates a random access procedure toward the eNB2 according to the signaling.
In this case, the handover selection procedure at the network side in step 102 needs to give consideration to various factors comprehensively, and the measurement report of the UE in step 101 is one of the factors. When the serving signal quality of the present cell is below one certain threshold and the signal quality of one certain adjacent cell reported by the UE is above one certain threshold, the network side can inform the UE to switch. However, in order to avoid abnormality from occurring, the network side further needs to acquire some other auxiliary information for reference. For example, in order to avoid ping-pong handover from occurring, when switching, the network side needs to carry the history information of the UE, which includes information of the stay time of the UE in a previous cell during the calling or service and the like.
Since the current handover selection procedure mainly depends on the measurement of the downlink serving signals of an adjacent cell reported by the UE and the uplink sending is not taken into consideration, abnormal situations such as radio link failure (abbreviated as RLF) and the like can happen. For example, if RLF happens in a target cell shortly after the handover of the UE, then the UE cannot successfully access eNB2 in step 104, and one reason for this RLF is the unsatisfied uplink sending of the UE in the target cell.
In addition, in the LTE system, in order to reduce the manual maintenance work load of the network and optimize the network capacity, in the requirements currently proposed by the Next Generation Mobile Network (abbreviated as NGMN) organization, the LTE needs to support the self-organized network (abbreviated as SON) function which includes the coverage and capacity optimization (abbreviated as CCO) function of the network, i.e. the parameter configuration of a cell can be modified automatically by the automatic configuration function and self-optimization function of the network so as to achieve the optimization of network coverage.
In order to optimize the network coverage, the network side first needs to detect the existence of the current network coverage. As shown in FIG. 2, cells A and B governed by eNB1 and eNB2 are adjacent with each other, however, the cell B has coverage problem at the junction. At this moment, when the UE in cell B moves to the area D shown in the figure, phenomena such as dropped calls will occur. Therefore, how to find this coverage area is also a problem to be resolved.